# Why does a buffer work best at the pH closest to its pKa?

I think I'm having trouble understanding exactly how the pKa relates here on a conceptual level. For example I know that carbonic acid works somewhat well as a buffer at pH near 7, since its pKa is relatively close, but why is that exactly?

• Welcome to Chemistry.SE! Take the tour to get familiar with this site. Mathematical expressions and equations can be formatted using $\LaTeX$ syntax. This question might be considered too broad since it is about the very principle buffer solutions are about. Please read the Wikipedia article first and try to narrow down your question. – Martin - マーチン Apr 21 '16 at 6:28

## 1 Answer

A buffer works best when there is the same amount of weak acid/base and its conjugate. If you look at the Henderson Hasselbach equation, and set the concentration of the weak acid/base equal to each other, pH=pKa.